Toxicity of endosulfan on embryo-larval development of the South American toad Rhinella arenarum.

Endosulfan is a widely used pesticide despite its extreme toxicity to a variety of taxa and its worldwide ban. The aim of the present study was to evaluate the acute and chronic toxicity of endosulfan on the embryonic-larval development of the common South American toad Rhinella arenarum. The results showed that lethal and sublethal effects increased with concentration and exposure time. The sensitivity to endosulfan increased during the larval period, the complete operculum stage (S.25) being the most sensitive (504-h median lethal concentration [LC50] = 0.01 mg endosulfan/L; 10% lethal concentration [LC10] = 0.004 mg endosulfan/L). Endosulfan exposure caused morphological abnormalities such as general underdevelopment, edema, gill malformations, and cellular dissociation as well as neurotoxicity. Our results also showed that larvae exposed to concentrations of 0.005 mg endosulfan/L and 0.01 mg endosulfan/L completed metamorphosis earlier than controls, but with underdevelopment. The 240-h teratogenic index was 6.13, implying a high risk for embryos to be malformed in the absence of significant embryonic lethality. Because the hazard quotients for chronic exposure were over 1, the level of concern value and toxicity endpoints obtained in the present study for R. arenarum occurred at concentrations lower than the levels of endosulfan reported in the environment, this pesticide should be considered a potential risk for this species.

Stage-dependent toxicity of bisphenol a on Rhinella arenarum (anura, bufonidae) embryos and larvae.

The acute and chronic toxicity of bisphenol A (BPA) was evaluated on the common South American toad Rhinella arenarum embryos and larvae by means of continuous and pulse exposure treatments. Embryos were treated continuously from early blastula (S.4) up to complete operculum (S.25), during early larval stages and by means of 24 h pulse exposures of BPA in concentrations ranging between 1.25 and 40 mg L(-1) , in order to evaluate the susceptibility to this compound in different developmental stages. For lethal effects, S.25 was the most sensitive and gastrula was the most resistant to BPA. The Teratogenic Index for neurula, the most sensitive embryonic stage for sublethal effects was 4.7. The main morphological alterations during early stages were: delayed or arrested development, reduced body size, persistent yolk plug, microcephaly, axial/tail flexures, edemas, blisters, waving fin, underdeveloped gills, mouth malformations, and cellular dissociation. BPA caused a remarkable narcotic effect from gill circulation stage (S.20) onwards in all the organisms exposed after 3 h of treatment with 10 mg L(-1) BPA. After recovering, the embryos exhibited scarce response to stimuli, erratic or circular swimming, and spasmodic contractions from 5 mg L(-1) onwards. Our results highlight the lethal and sublethal effectsof BPA on R. arenarum embryos and larvae, in the last case both at structural and functional levels.